The invention concerns a proportional, pressure control valve, with functions for pressure reducing and for the maintenance of a given pressure. The valve is comprised, essentially, of a valve housing, with entry and exit ports, a control element for the opening and closing of an orifice type opening, an armature rod with an armature axis for the connection of the control element with a proportional magnet. The proportional magnet is an assembly of a magnet core, a magnetic armature rod and a magnet coil. The magnet armature is movable, back and forth, between two end positions in the direction of the armature axis. In this situation, the first end position represents a stop position of the, magnet, wherein the magnet armature holds the control element immobile in this position.
Valves of the above described construction are, in manifold forms, known within the state of the technology. These valves are, for one instance, applied as direct control valves for the regulation of clutches in automatic motor vehicle gear shifting transmissions. Where commercial vehicles were concerned, in such transmissions, the principal hydraulic pressure, otherwise (and hereinafter) known as the xe2x80x9csystem pressurexe2x80x9d, runs about 24 bar. This system pressure is commonly, by means of a pressure reduction valve, reduced to a pilot control level, to which the proportional pressure control valve is subjected. In order to hold this valve closed, following the engagement of a clutch, normally an elevated safety pressure, which approximates the said system pressure, is applied to the clutch cylinder, and held at this level, for instance, by means of additional check valves. The operation of this arrangement, demands, for one clutch in an automatic transmission, the installation of up to three valves, namely, a proportional pressure control valve, a pressure reducing valve, and a check valve.
The purpose of the present invention is to make available a valve, which fulfills the above named functions, but has a simpler construction achieved by fewer components, and accordingly, is less expensive in its manufacture.
In accord with the invention, this purpose is achieved, in that, with a proportional pressure control valve of the aforesaid type of construction, and when in the pressure holding position of the magnet armature, the smallest possible axial distance is so measured between the two opposingly situated end surfaces of the magnet armature and the magnet core, that the magnetic force between the magnet armature and the magnet core., in this said holding position, is greater than the magnetic force in the operational area of the proportional magnets and that, the mag net armature, by means of the increased magnetic force, can be fixed in this position. The invention advantageously makes use of this situation, in that a proportional magnet, in its operational range, exhibits a nearly horizontal force stroke characteristic line and the magnetic force, in a zone below the level of a defined stroke, that is, a distance between magnet armature and magnet core, climbs rapidly as compared to the said magnetic force in its operational range. For the state of the technology, refer also to Mannesman-RexRoth, (German text), xe2x80x9cFluid Technologyfrom A to Zxe2x80x94The Hydraulic Trainerxe2x80x9d, Vol. 5, May 1995. page 266. By means of these magnetic characteristics with large magnetic forces at very small air gap distances it becomes possible, with the proper magnet design, to energize a coil current, i.e. a xe2x80x9csnap currentxe2x80x9d, with which the operational zone of the magnet is overridden and the magnet armature is held in the zone of the high magnetic force. By means of the connection of the magnet armature through its armature rod with the control element, in this way, the holding force of the control element is increased to such a level, that this element, even when subjected to continuous system pressure of 24 bar, remains reliably in its holding position. This is because the hydraulic force, which acts in one direction of the control element is less than the magnetic force which opposes it.
The valve is additionally constructed in such a way, that in the holding position, advantageously the inlet port to the valve and the service connection to the clutch are both open and the hydraulic system pressure, to its greatest extent, is exerted against the said clutch. On this account, and with the proportional pressure control valve of the invention, both the pressure reducing valve as well as the pressure holding valve can advantageously be dispensed with. This is because the functions of these valves have been replaced by the invented valve. Furthermore, a controller of this kind, advantageously possesses a high pressure to coil current (pI) resolution in its fine adjustment range between 0 and 12 bar. Further, the invented holding function enables, advantageously, the blocking of oscillating masses in the pressure control arrangement, whereby an increased vibration stability along with a reduced mechanical ablation is achieved.
In a preferred development of the invention, the control element exhibits three control edges. This control element is designed as a double action piston with two sliding edges and one additional tight seat. The surface of said seat extends itself in a radial direction relative to the longitudinal axis of the control element. In this way and in a very simple manner, is achieved an economical construction of a 3/2-way pressure regulator, serving as a direct control valve with a magnetic holding function of the magnet armature in zero-flow design (ZF), wherein the radial seat is provided for the fulfillment of an improved sealing function, namely zero flow in respect to leakage flow.
In a shut-off development of the invention, the proposal is made, that the control element, i.e. the said valve piston, is provided with an internal pressure feedback. This is created, in that the double action piston possesses a piston boring with a damping element, for instance, a damping plunger, whereby, advantageously, an additional damping function is made possible. The double action piston, the armature rod, the magnet armature, the magnet core and the valve housing, in regard to their axial length, are so well integrated, and the fastenings of the double action piston, of the armature and armature rod are chosen in such a manner relative to the magnet core, so that the smallest axial space between the magnet core and the magnet armature lies in a range of 0 to 0.3 mm, preferably ca. xe2x89xa60.1 mm.
At this spacing, the magnetic force is sufficiently elevated above the magnet force in the operational area, so that the magnet armature and therewith also the double action piston, by means of the available hydraulic system pressure are advantageously held in their end position.
Alternative to the above described realization of the smallest possible spacing between the magnet core and the magnet armature, in a particularly advantageous design of the invention, a spacer disk made of non-magnetic material is placed between the magnet core and the magnet armature. By means of such a disk, which prevents a xe2x80x9cmagnetic adherencyxe2x80x9d of the magnetic armature onto the magnetic core, by means of varied designs of the disk thickness, favorably, a simple adjustability of the magnetic force becomes possible. Alternative to the spacer disk, a non-magnetic coating on the magnet core and/or on the magnet armature can be provided to maintain the desired axial air gap.
In an advantageous construction of the pressure control valve, the distance between the two end surfaces of the magnet core and the magnet armature runs some 0.01 to 0.3 mm, although this is preferred to be xe2x89xa60.1 mm.
In yet another alternative design of the already described proportional magnets, the armature rod is installed to be axially slidable in the magnet armature and is subjected to the force of a compression spring.
Advantageously, the compression spring possesses a spring force, which is equal to, or greater than the maximal hydraulic control force on the double acting piston and thus exerts the spring force through the armature rod in a contrary direction.
In another development, the proposal is, that the compression spring possess the least possible spring rate, which is so measured out, that even in the case of a small coil current, the magnet armature can be brought into the area of higher magnetic forces, and thereby the holding function can be realized.
In a special development of the invention, it is proposed, that the armature rod possess an axial detent surface, which is situated, so that if the armature finds itself in the proportional area of the magnet, the detent surface projects by a defined distance over that end surface of the magnet armature which is proximal to the magnet core. Thereby, the advantageous achievement is, that the magnet armature in the proportional area does not move into the area of high magnetic forces, since the armature rod, with its detent surface comes to rest on the end surface of the magnet core, and the said magnet core must, on this account, remain separated. The compression spring, placed in series with the armature rod, makes possible thus, a snap protection without loss of magnetic force, since the already stressed spring exceeds the hydraulic-magnetic forces, as long as these are less than the preloaded force of the compression spring. If, it should so happen, in the pressure control or proportional zone of the magnet armature comes to a critical operational condition, for instance, a system pressure breakage, then the armature moves itself immediately in the direction of the magnet core. A move of this kind is terminated by the said detent surface of the armature rod, as long as the proportional magnet is still located in its proportional operational area and thus the magnet armature remains at a distance from the magnet core.
Should there be need for the magnet armature to controllably enter the hold situation, by means of an increase in the coil current for a short period, the magnetic force is brought to a value higher than that of the maximum hydraulic control force. In accord with this, the spring packet is further compressed, until the end surface of the magnet armature moves along with the detent surface of the armature rod, and in this way can be brought into the magnetic holding area.
In a further development of the invention, it is proposed, that the magnet coil be connected with an electrical control apparatus, which, in specifiable, periodic intervals, emits a current impulse to the magnet coil for the maintenance of the holding position.
In this way, assurance is provided, that the magnet armature retains its holding position relative to the magnet core and does not unexpectedly drop out of the holding position and that advantageously, the control element reliably remains in its own holding position.
It has shown itself as being of advantage, if the current impulse possesses sufficient strength, which corresponds to a snap current and is greater than the holding current of the magnet coil and for instance, measures about 950 mA and; that the current impulses occurs in time periods of, for example, 20 ms. The valve design should, ideally, be so conceived, that upon unexpected drop outs,the switching elements nevertheless remain in the closed position, that is, for example, the control pressure remains at 12 bar.
For the intended release of the magnet armature from the holding position, the magnet coil is subjected to an electrical control signal, which, for instance, is carried out as a reduction and then subsequent increase (loop control) of the control current in the magnet coil. In this way, and in a simple manner, an elegant means of a release of the armature can be effected.
As an alternative, a voluntary release of the magnet armature from its holding position can be accomplished by an increase of the hydraulic system pressure to a value above the holding pressure.
In this case, the pressure increase acts, for example, on the feedback and especially on the end of the piston boring. In this way, and in an advantageous manner, by means of a movement of the armature rod, a release of the magnet armature from the magnet core is achieved.
In an advantageous manner, the invented proportional pressure regulating valve is employed as a direct control valve. When this is done, the valve is preferably designed as a 3/2-way proportional pressure valve with a magnetic holding function of the magnet armature, so that, when the invented valve is used, then both a pressure reducing valve as well as a pressure holding valve can be done away with.